Detection systems exist for detecting signals generated by emitters which are of interest. For example, there are scanners (e.g., a police scanner) that are capable of scanning a frequency band for transmissions within that frequency band. In the case of a police scanner, channels are scanned sequentially to find a signal of interest. Scanning is achieved by tuning receiver hardware to a particular frequency to observe one or more transmissions within that particular frequency.
There are more sophisticated systems to detect transmitted signals that use other methods for determining signals of interest. For instance, there are what are referred to as Electronic Support Measures/Electronic Intelligence (ESM/ELINT) systems for conducting surveillance (e.g., radar, and other signals across a wide range of frequency spectrums). These systems detect one or more signals produced by emitters (often called “threats”) that are detected and observed.
For example, in a military aircraft or other vehicle, enemy signals (e.g., radar) may be observed that are capable of detecting the vehicle (e.g., an airplane). These threats may need to be determined prior to detection to ensure the safety of the vehicle, and are often observed and classified to identify the particular threat. For example, certain signals may have particular signatures that are indicative of certain types of emitters. Further, there may be a need to detect and identify the location of a threat (e.g., a radar installation) for targeting purposes.
There is a problem in that there may be multiple threats but only a finite number of resources to detect them. More particularly, there may be hundreds of threats, but receiver capabilities do not allow all threats to be observed simultaneously at all frequencies. However, there is a need to scan the frequency spectrum in an efficient manner to detect all of the signals of interest. In some cases, there is a need to have assurance that a threat will be detected in time to respond to that threat. In the case of detection of a radar emitter by a vehicle, it may be also necessary to detect the threat before the threat is capable of detecting the vehicle.
There is difficulty in balancing the need for detecting each of numerous possible threats because of the finite resources of the detection system. That is, hardware and/or software (e.g., memory, processing capability, etc.) of the detection system may be limited to monitor only certain portions of the frequency spectrum of interest or may be limited to detecting a limited number of threats. Practically, there are a number of threats that are concurrently transmitting that should be detected, but it is expensive from a hardware standpoint to monitor all frequencies of interest at all times to detect all threats simultaneously. For example, U.S. Pat. No. 6,020,842 discloses one method for improving the probability of intercepting data transmitted in a number of different frequency bands. In summary, there is a continuing need for improved methods for detecting and analyzing emitter signals.